Zoology Lab
MICROSCOPY
Objective:
1. To learn how to use both a dissecting and a compound microscope effectively and efficiently (lighting, focus, magnification, resolution), and to practice manipulating small organisms
Principals:
1. The smallest object viewable under a compound light microscope is limited by resolution or resolving power (ability to distinguish between two nearby points) and not magnification.
2. Mircoscope resolution is limited by the wavelength of the source of illumination (visible light, in the case of an optical microscope) and the numerical aperture of the lenses.
Smallest object viewable limited by resolution which is limited by wavelength of the source of illumination and N.A of the lenses.
Lab:
Stero microscope low power instrument used in visualizing large objects at low magnification (5-50X); produces unreversed, right side up, 3-d image; unlike the compound microscope. 1. Prepare slide 2. Turn on transformer 3. Use lowest power lens 4. One eye closed, find and focus the object sharply 5. Close eye open the other 6. Keep both eyes open when viewing object
Compound microscope Magnifies to about 1000 times with some modification, can be increase 2-3 times (but that’s about the limit)
The smallest viewable object is limited by resolution and not magnification. Theoretically, resolution (cloest two points can be together and still distinguished as two separate points) can be determined by the formula:
Resolving power = wavelength of light/ (2 * NA)
NA = numerical apiture, less than one when object is dry, = 1.25 when using oil
The numerican aperture is the product of the refratice index of the medium between the front lens of the objective and object being examined and the sin of half the angle formed by the rays of light entering the front lens from a point on the object (0.5 A)
N.A = n * sin * (0.5 A)
Visible light ranges between 400-700nm ; NA less than one for dry, about 1.25 for oil.
Main point: limited by
Objective:
1. To learn how to use both a dissecting and a compound microscope effectively and efficiently (lighting, focus, magnification, resolution), and to practice manipulating small organisms
Principals:
1. The smallest object viewable under a compound light microscope is limited by resolution or resolving power (ability to distinguish between two nearby points) and not magnification.
2. Mircoscope resolution is limited by the wavelength of the source of illumination (visible light, in the case of an optical microscope) and the numerical aperture of the lenses.
Smallest object viewable limited by resolution which is limited by wavelength of the source of illumination and N.A of the lenses.
Lab:
Stero microscope low power instrument used in visualizing large objects at low magnification (5-50X); produces unreversed, right side up, 3-d image; unlike the compound microscope. 1. Prepare slide 2. Turn on transformer 3. Use lowest power lens 4. One eye closed, find and focus the object sharply 5. Close eye open the other 6. Keep both eyes open when viewing object
Compound microscope Magnifies to about 1000 times with some modification, can be increase 2-3 times (but that’s about the limit)
The smallest viewable object is limited by resolution and not magnification. Theoretically, resolution (cloest two points can be together and still distinguished as two separate points) can be determined by the formula:
Resolving power = wavelength of light/ (2 * NA)
NA = numerical apiture, less than one when object is dry, = 1.25 when using oil
The numerican aperture is the product of the refratice index of the medium between the front lens of the objective and object being examined and the sin of half the angle formed by the rays of light entering the front lens from a point on the object (0.5 A)
N.A = n * sin * (0.5 A)
Visible light ranges between 400-700nm ; NA less than one for dry, about 1.25 for oil.
Main point: limited by